1. Field of the Invention
The present invention relates to an interference fit type cutting tool having a tool holding section and a tool mounted therein.
This specification is based on patent applications filed in Japan (Japanese Patent Applications Nos. 10-350404 and 11-123211), and the descriptions in the Japanese applications are incorporated as a part of this specification.
2. Background Art
Conventionally, a cutting tool is known as an example of this type of cutting tool, in which a projection is formed in one of an edge section and a shank section, a recess is formed in the other section, and the projection and the recess are fitted by shrinkage fitting.
In a case in which the cutting tool is, for example, a milling tool such as an endmill, the shank section is made of, for example, steel, and the edge section is made of cemented carbide or the like and is detachably and replaceably fitted by shrinkage fitting. By making the edge section replaceable, edge sections having different types of cutting edges can be mounted.
When producing such a cutting tool using shrinkage fitting, while the shank section with a recess having a substantially high coefficient of thermal expansion is heated, the recess and a projection of the edge section are fitted together. In this case, when the shank section having the recess is heated to, for example, approximately 200xc2x0 C., the recess is thereby expanded so that the inner diameter exceeds the interference for fitting to the projection, and is allowed to be fitted.
When the edge section is detached from the shank section in the fitted cutting tool, however, if the shank section having the recess is heated, the edge section having the projection is simultaneously heated and is thermally expanded. Therefore, the shank section must be heated above approximately 300xc2x0 C. to detach the edge section, and this is inefficient. Furthermore, when there is a small difference in coefficient of thermal expansion between the materials of the edge section and the shank section, it is more difficult to detach the edge section.
As a method of overcoming such problems, a technique has been disclosed and proposed in Japanese Unexamined Patent Publication No. 10-34408.
In this method, a space is formed over the entire periphery of a fitting section between a projection and a recess of an edge section and a tool holder that are fitted together, the edge section is pushed by supplying hydraulic pressure into the space during heating, and is thereby detached from the tool holder. Another means has also been proposed in which a tool holder is provided with a communication hole that extends to a fitting section, and a rod is inserted in the communication hole in a heated state and is struck with a hammer to apply impact, thereby detaching the edge section.
In the above-described detaching method using hydraulic pressure, however, a high-temperature state is established by heating when detaching the edge section, and there is a danger that oil will ignite, and waste oil disposal is necessary. In the method using the rod for striking, since the communication hole forms a space during cutting, stiffness and strength of the tool are deteriorated, rotation balance may be upset, and whirling may be caused by vibration. Furthermore, there is a danger that the edge section will be chipped due to impact resulting from being struck by the hammer, that the service life will be shortened, and that an operator will suffer burns.
An object of the present invention is to provide a safe interference fit type cutting tool that does not affect the environment and does not shorten tool life.
Another object of the present invention is to improve workability in replacing a tool, a tool holding section, or the like in a cutting tool.
An interference fit type cutting tool according to the present invention includes a tool and a tool holding section that are detachably fitted together, wherein a presser section is provided to separate one of the tool and the tool holding section from the other.
When detaching the tool after interference fitting, the fitting strength is weakened by heating or cooling the interference-fitted section, the tool and/or the tool holding section is directly or indirectly pushed by operating the presser section, and one of the tool and the tool holding section is separated from the other, whereby the tool or the tool holding section can be detached.
According to a preferred embodiment of the present invention, one of the tool and the tool holding section has a projection, and the other has a hole portion to be fitted on the projection. One of the projection and the hole portion has an interference, and a presser member serving as the presser section is mounted in one of the tool and the tool holding section so as to press the other.
By pushing the projection or the hole portion by the presser member while the fitted portion between the projection and the hole portion is heated and cooled, the tool and the tool holding section can be separated from each other.
According to another preferred embodiment of the present invention, the presser member is in threaded engagement with a threaded hole formed in the tool holding section and is able to push the tool.
Since cutting is performed with the presser member in threaded engagement with the threaded hole, tool stiffness and strength are not lowered. In the case of a milling tool, it is possible to avoid the dangers of upsetting the rotation balance and of whirling due to vibration. Detachment of the tool is safe and does not result in a problem of waste oil disposal and the like because a hydraulic mechanism or the like is not used. Furthermore, since the tool is pushed by the presser member without being struck, it will not be chipped, and the service life thereof will not be shortened.
According to another preferred embodiment of the present invention, an intermediary member is provided in a space formed between the tool and the tool holding section, and the presser member is placed to push the intermediary member, and to push at least one of the tool holding section and the tool via the intermediary member.
By providing the intermediary member in the space, it is possible to make the presser member small, and to pull out one of or both the tool and the tool holding section.
According to a further preferred embodiment of the present invention, the tool and the tool holding section have projections, and both the projections are fitted and connected by a connecting member. One of the projections and the connecting member has an interference, and a presser member serving as a presser section is mounted in one of the connecting member, the tool, and the tool holding section so as to press at least one of the tool holding section and the tool.
Therefore, the tool or the tool holding section can be detached by operating the presser member to push the tool or the tool holding section while the connecting member is subjected to heating or other processes. Since a hydraulic mechanism or the like is not used in the operation of detaching the tool or the tool holding section, the operation is safe and the problem of waste oil disposal does not arise. Furthermore, since the tool or the like is pushed by the presser member without being struck, it will not be chipped, and the service life thereof will not be shortened.
According to a further preferred embodiment of the present invention, an intermediary member is provided in a space formed between the projections of the tool and the tool holding section and the connecting member, and the presser member is placed to push the intermediary member, and is able to push at least one of the tool holding section and the tool via the intermediary member.
The placement of the intermediary member in the space allows the presser member to be small.
According to a still further preferred embodiment of the present invention, the presser section is a stepped portion formed by making the diameter of at least a part of the base end portion of the tool larger than that of the leading end portion of the tool holding section.
When the tool is drawn out of the tool holding section, the interference-fitted section is heated or cooled, and a jig can be pulled out while being caught by the stepped portion of the tool, which allows the tool to be easily separated. Moreover, this stepped portion ensures a clearance between the tool holding section and a workpiece, which smoothes the movement of the cutting tool and the discharge of chips.
According to a further preferred embodiment of the present invention, the tool and the tool holding section have projections, and both the projections are fitted and connected by the connecting member. One of the projections and the connecting member has an interference. The presser section is a stepped portion formed by making the diameter of at least a part of the base end portion of the tool larger than that of the leading end portion of the tool holding section.
According to a still further preferred embodiment of the present invention, a cutting edge is provided in the stepped portion.
According to this structure, cutting can also be performed with the cutting edge provided in the stepped portion even when the cutting tool is pulled back, which facilitates finishing and lifting of the cutting tool.